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Author Topic: Does gravity have a finite speed, if so how could it be measured?  (Read 4657 times)

Offline oatman

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Wondered this for a while, and I suppose also whether magnetism and other forces have a speed.

The speed of light applies to anything with mass, i think! But does a graviton have mass, if so why cant we find them?...thanks!

 ???
« Last Edit: 30/03/2011 13:47:22 by oatman »


 

Offline Jolly- Joliver

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Wondered this for a while, and I suppose also whether magnetism and other forces have a speed.

The speed of light applies to anything with mass, i think! But does a graviton have mass, if not why cant we find them?...thanks!

 ???

They're expressed in strengths. I suppose you could relative to an impostion give a pull speed.
 

Offline imatfaal

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Gravitational waves travel at the speed of light - this is a classical effect from GR.  The graviton is massless chargeless gauge boson that can be seen as the mediator of gravity in non-classical theoroes - it would also travel at the speed of light.  You can think of gravitational waves as the classical limit of the graviton - ie where qft becomes too unwieldy and GR will give practically the same results.  At present there is very good experimental evidence for GR whilst the graviton is hypothetical, but the existence of one does not preclude the other.  We are unlikely to detect a single graviton - but we are actively searching for gravitational waves, and hopefully might soon get confirmation.
 

Offline syhprum

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Not everyone agrees, I have an open mind on the matter, I was convinced but now I have doubts.


http://www.metaresearch.org/cosmology/speed_of_gravity.asp
 

Offline imatfaal

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If you want to disagree with GR then feel free - but very few do and all the experimental evidence follows the predictions of GR.   Van Flandern made some important discoveries that were rejected for many years - but his denial of GR and other off the wall theories (faces on mars etc) are so beyond mainstream to be slightly crackpot. 
 

Offline yor_on

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Ahh, he's interesting :) And rebutted, at least when it comes to gravity. But 'Gravity' is a weird, weird property, and I was quite impressed reading his arguments myself. But here is a earlier thread we had with A rebuttal.
 

Offline oatman

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thanks for all the input, and interesting article!

newbielink:http://www.metaresearch.org/cosmology/speed_of_gravity.asp [nonactive]
[/quote]
 

Offline Phractality

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The mainstream majority is divided on this question. Some say the speed of gravity is the speed of light; others say it has no speed, being instantaneous. As I see it the question boils down to the direction in which the force vector of gravity points. But the word "force" ain't in the lexicon of GR. GR does recognize the existence of momentum, though. I suppose someone with a good grasp of GR could calculate the change of the momentum vector for a planet near a black hole for a very short time interval; the direction of the change is the direction of the force of gravity. If the force vector points exactly toward the center of the black hole, then the speed of gravity force is infinite.

Any claims of a finite speed other than light speed are new theories, so maybe this thread should be moved there.

Van Flandern made some important discoveries that were rejected for many years - but his denial of GR and other off the wall theories (faces on mars etc) are so beyond mainstream to be slightly crackpot.

I have to agree that VanFlandern had some crackpot theories, like spontaneously exploding planets, for example. Nevertheless, I am persuaded that he was right about the speed of gravity. The force of gravity definitely does not point in the direction where we see the sun; if it did, it would pull us into higher and higher orbits, and solar systems could not exist. So it can't be the speed of light.

If VanFlandern had had a better understanding of the difference between Euclidean space and Minkowski space-time, he might have argued his points more convincingly. As I see it, both VanFlandern and GR may be correct; they only seem to contradict one another because they are using the same words to mean different things. When Minkowski redifined "straight line", he tacitly changed the meanings of all the old familiar parameters. The mainstream point of view seems to be that Minkowski eliminated the existence of Euclidean space; I believe both types of space are valid, but they are merely mathematical analogies of physical space.

I believe both e/m waves and gravity waves propagate at light speed, but the forces associated with them are as fast as VanFlander said they are, at least in Euclidean space. I don't have sufficient understanding of GR to say whether they are faster than light in Minkowski space-time. Measuring the speed of gravity (and all the other forces) is extremely difficult.

If I am right about all the forces having the same FTL speed, then it should be about 10^44 times easier to measure the speed of electrostatic force, and then translate that to gravity force. The trouble is that you can't relocate an electrostatic charge instantaneously; you can only accelerate it from A to B at sub-light speed, and when you do so, you get an electromagnet wave which overwhelms your attempts at measureing the electrostatic force. There have been attempts to do so, and even claims of success, but no widely accepted proof. I'm pretty sure I have seen a more credible source, which placed it at 3 x 10^10 c, but for now I can only find this [urlhttp://www.holoscience.com/synopsis.php?page=11]Electric Universe [/url] source, which places it at about 8 x 10^13 c. VanFlandern's estimate was > 2 x 10^10 c.
 

Offline syhprum

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Thanks, I was beginning to feel like a heretic daring to doubt GR.
I am not the stuff matyrs are made of it would only take the mildest of "enhanced interrogation" to get me to recant
 

Offline yor_on

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Read this one too. Then decide for yourself. A rebuttal to Van Flandern; Aberration and the Speed of Gravity

But I believe the question was about 'gravitons' :)"does a graviton have mass, if so why cant we find them?" Imatfaal gave us a nice description, and here is how CERN looks at their search for the HIGGS and Gravitons from 2000. Supersymmetry and the Standard Model. Reading it one need to remember one thing though. It's not surprising that GR and QM is at odds with each other, one is searching for quanta explaining it all, whilst General relativity describe gravity as a geometric property of space and time. So to do as the article, sounding surprised over the fact that they don't 'fit' is not that cool. GR has a very good description of gravity. QM do not, as for now, and if their experiments can prove gravity as 'particles', I'm not sure how GR will 'fit' any more?
« Last Edit: 30/03/2011 23:40:33 by yor_on »
 

Offline syhprum

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A recent article in the SCIENTIFIC AMERICAN suggested that the mass of the Graviton was 10^-11 that of the neutrino hence quite undetectable.
 

Offline CPT ArkAngel

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The force of gravity could be generated by spacetime itself (variations in spacetime density). The best way to measure its propagation velocity is by measuring variation in timerate... I would bet on the speed of light. The inflation theory of the Universe would take a fatal shot if not...

A body with mass does not loose energy by gravity. If gravity propagates one way, it should propagates something in return... attraction...
« Last Edit: 31/03/2011 10:54:05 by CPT ArkAngel »
 

Offline imatfaal

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Syhprum - I am not sure that heresy is the best way of describing it, but I know what you mean.  I disagree with you, but I know what you mean; the immense pressure to conform to scientific mainstreamism is damaging, it creates doubt through its own need to say everything else must be wrong.  The better method of defence is "GR works, bring me something else that works and I will try that too"  there is no other consistent theory that will let you put a satellite into orbit around mercury, get the gps atomic clocks working properly, and correctly predict the amount of gravitational lensing etc.  As soon as the non-classical theories were shown to have great predictive power it became clear that GR cannot be the whole story because of the contradictions between the two - but in the classical limit GR works blindingly well. 

and do you have a link to the SciAm article - I would love to read it
 

Offline syhprum

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Imatfaal

"and do you have a link to the SciAm article - I would love to read it"

I cannot find a reference to the SCIENTIFIC AMERICAN article but I think it was a somewhat simplified version of this paper for lay readers


http://arxiv.org/PS_cache/gr-qc/pdf/0601/0601043v1.pdf
« Last Edit: 31/03/2011 13:44:51 by syhprum »
 

Offline imatfaal

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Imatfaal

"and do you have a link to the SciAm article - I would love to read it"
I cannot find a reference to the SCIENTIFIC AMERICAN article but I think it was a somewhat simplified version of this paper for lay readers

http://arxiv.org/PS_cache/gr-qc/pdf/0601/0601043v1.pdf

Thanks - Although I could probably only really understand the mellowed down version for the laity
« Last Edit: 01/04/2011 13:44:44 by imatfaal »
 

Offline JP

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Syhprum - I am not sure that heresy is the best way of describing it, but I know what you mean.  I disagree with you, but I know what you mean; the immense pressure to conform to scientific mainstreamism is damaging, it creates doubt through its own need to say everything else must be wrong.  The better method of defence is "GR works, bring me something else that works and I will try that too"  there is no other consistent theory that will let you put a satellite into orbit around mercury, get the gps atomic clocks working properly, and correctly predict the amount of gravitational lensing etc.  As soon as the non-classical theories were shown to have great predictive power it became clear that GR cannot be the whole story because of the contradictions between the two - but in the classical limit GR works blindingly well. 

Well put.  It's a big problem for alternative theories that there are so many crackpot theories out there.  It's difficult at times to take the 1% of theories with actual substance seriously when 99% of them have no scientific content.  There are, for example, several legitimately scientific explanations for "dark energy" and "dark matter."  (Some have more evidence than others, but multiple theories are being considered by scientists because they show promise.)  There are also many different interpretations of what the mathematics of quantum mechanics actually means.  String theory might also be considered to be non-mainstream, but it does conform to experiments and is trying hard to be testable experimentally.

Really, if your theory is any good, you should be able to point to evidence that it's right.  Anyone who tries to push their theory by making claims about how the "mainstream orthodoxy" is preventing it from being accepted is just shooting themselves in the foot--as that claim is mostly used to distract from the fact that the theory has no scientific basis.

----------------------------------------------------

There's currently searches for gravitational waves (for ex. LIGO: http://www.ligo.caltech.edu/).  If these waves are found and agree with general relativity's predictions, then we can be pretty confident that gravity moves at the speed of light.  We may even be able to measure the speed of the waves via experiment.  Gravitons are much more elusive because they're so small and interact much more weakly with matter than do photons or other force-carrying particles.  Just think of how easy it is to see light coming from distant stars, while we've spent years constructing highly sensitive devices in order to detect gravity waves coming from them.
 

Offline Phractality

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There's currently searches for gravitational waves (for ex. LIGO: http://www.ligo.caltech.edu/).  If these waves are found and agree with general relativity's predictions, then we can be pretty confident that gravity moves at the speed of light. 

That's like saying, "If we can measure the speed of transverse waves on a wire suspended in zero gravity, then we can be pretty confident that is the speed of longitudinal waves on that same wire." I know of no one who disputes the theory that gravity waves should propagate at the speed of light, but there are plenty who dispute that gravity force propagates at the speed of light. 
 

Offline yor_on

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It depends on how you think of gravity methinks. Let it be a 'field' and you can still have something 'propagating' in it as a distortion. and as the speed of light is the upper limit of 'motion' it makes perfect sense to expect this distortion to move at that speed too. But rather than to have it as a field I prefer to look at as both the back, and the foreground, of SpaceTime.

With us, soo stuck right in the middle of it :)
 

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